1. Field of the Invention
This invention relates to a hydrocyclone separator, and more particularly to such a separator in which a solid core is positioned within the entrance of a vortex finder tube.
2. Background of the Invention
Hydrocyclone separators are fixed wall centrifugal density separators. The body is stationary and rotation is initiated by the pressurized fluid flow. Hydrocyclone separators utilize fluid pressure energy to generate rotational fluid motion. This rotational motion causes relative movement of suspended materials or particles in the fluid, permitting separation of these materials. The influence of centrifugal force moves the more dense particles outwardly toward the wall of the separator while the less dense particles move radially inward with the dominant liquid medium.
Hydrocyclone separators generally have a tangential feed inlet that is perpendicular to two opposed vertical axial outlets; one at the bottom end of the separator and the other at the upper end of the separator. The lower outlet is for dense components of the fluid. The outlet at the top of the hydrocyclone separator includes a tube that extends downwardly into the main central chamber of the separator and is referred to as a vortex finder tube. The vortex finder tube functions as the outlet for the separated and relatively clean liquid accompanied with the light gravity components of the fluid.
The sharpness of separation in hydrocyclone separators heretofore has been relatively low in efficiency, because of the intermixing of coarse particles with fine particles in the fluid or slurry during the separation process. This intermixing results from the flow characteristics in hydrocyclone separators which includes an outer vortex or helical flow and an inner vortex or helical flow. The outer helical flow is caused by the rotation of the fluid that generates the centrifugal force to move the more dense particles toward the outside wall of the hydrocyclone separator. The inner helical flow is created when all of the spinning fluid can not exit the relatively small orifice in the bottom outlet. The inability of all the fluid to exit at the bottom outlet causes a reversal flow creating an air core. The air core accelerates the inward generally radial movement of the lighter particles and the liquid phase of the fluid or slurry located along the central longitudinal axis of the separator.
The hydrocyclone separator may be positioned in either a horizontal or vertical position and the central axis may extend horizontally or vertically. The terms "upper" and "lower" are interpreted as including the opposed ends of the separator when the longitudinal axis of the separator extends in a horizontal direction or direction other than a vertical direction.
The amount of radial movement or migration of particles increases as the cross-sectional area of the central chamber decreases toward the lower end of the separator. Since all of the slurry (fluid having entrained solid particles) cannot exit the relatively small lower orifice, the fluid reverses its downward velocity direction and spins upwardly in an inner helical flow for discharge from the upper end of the vortex finder tube. The reversal applies only to the vertical component of velocity and the helical flows rotate in the same circular direction.
In the inner helical flow, a short-circuit flow often develops. It is well known to those skilled in the art that some of the inlet slurry moves along the internal roof or upper wall surface, down the outside wall of the vortex finder, and out the lower outlet without the components being separated. This is known as "short-circuit flow" or leakage. The short-circuit flow also influences some coarse particles directly into the overflow for discharge from the upper outlet without any separation. This indicates that reducing (or even eliminating) the short-circuit flow is beneficial to improving the sharpness of separation of the inner and outer vortices in a hydrocyclone. In addition, because of the existence of turbulence in a conventional hydrocyclone, and fluid flow along the peripheral surface defining the main chamber, some fine particles are retained in the underflow for discharge from the lower outlet, resulting in a drop in the separation sharpness.
Recent experimental research on the motion of solid particles in a hydrocyclone has shown that some light gravity particles in the inner helical flow move towards the outer peripheral surface in the cylindrical section. Indications are that some coarser particles are drawn toward the inner helical flow or vortex. The short-circuit flow can be as much as 15% of the processed flow rate that enters the vortex finder tube without separation. Expediting the centrifugal settlement of the particles in the inner helical flow in the cylindrical section is beneficial to improving the sharpness of separation between the inner and outer vortices.
To achieve a state of smooth flow in the hydrocyclone, the incoming feed should not collide with the circulating flow. In a straight tangential feed inlet, the inlet feed meets the circulating flow, generating turbulence in a critical region of separation.
In hydrocyclone classification, the interface between the outer and inner helical flows is often unstable because of a fluctuating air core. An unstable and fluctuating air core, much like the movement of a tornado, influences the intermingling of multi-density particles. This instability causes some of the more dense particles to be drawn into the inner helical flow and exit out the upper outlet defined by the vortex finder tube with the majority of the light gravity solids and some of the lighter particles migrating to the outer helical flow for discharge from the lower outlet thus attributing to an inefficient separation sharpness.
U.S. Pat. No. 3,105,044 dated Sep. 24, 1963 shows a hydrocyclone separator in which a solid core is positioned within the entrance of a vortex finder tube. A hollow inner vortex is formed with the diameter of the vortex dependent primarily on the rotational speed of the liquid mass, the pressure loss, and the diameter of the vortex finder tube orifice. The solid core has a diameter that is greater than the diameter of the hollow vortex or air core. An embodiment of the separator of U.S. Pat. No. 3,105,044 shown in FIG. 3 has a solid core with a diameter that constantly increases from its upper end to its lower end while the vortex finder tube tapers in a downward direction.